An optical semiconductor element such as a light emitting element or a light receiving element, or a semiconductor element such as a signal processing arithmetic element is housed in a semiconductor element package in order to protect the semiconductor element, and to connect the semiconductor element and external wiring.
A package described in Patent Literature 1 includes a terminal structural body for signal transmission and a receptacle body which supports the terminal structural body. The terminal structural body is configured so that an upper face signal conductor layer and an upper face ground conductor layer are formed on an upper face of a terminal block formed of a dielectric material, a lower face ground conductor layer is formed on a lower face of the terminal block, and a side face signal conductor layer and a side face ground conductor layer are formed on a side face of the terminal block. The lower face ground conductor layer has a non-forming region corresponding to the side face signal conductor layer, and a dielectric layer provided on the lower face of the terminal block has a non-forming portion corresponding to the non-forming region.